The Solar System

• What is the solar system a part of?

  The Milky Way galaxy
• What is at the center of the solar system?

  The sun
• How many main planets orbit the sun?

  Eight
• Name the four inner rocky planets.

  Mercury, Venus, Earth, Mars
• What are the four outer planets classified as?

  Larger gas giants
• What other objects are found in the solar system besides planets?

  Moons, asteroids, and comets
• What are moons classified as?

  Natural satellites
• How many moons do most planets have?

  At least one
• What is a galaxy?

  A massive group of stars
• How many stars does the Milky Way contain?

  Hundreds of billions
• How many galaxies are estimated to be in the universe?

  Hundreds of billions
• From what do stars like the sun form?

  Clouds of dust and gas
• What is a cloud of dust and gas called?

  A nebula
• What is the main gas in a nebula?

  Hydrogen
• What happens to the nebula in the first stage of star formation?

  It collapses due to gravity
• What is formed when the nebula collapses?

  A protostar
• What occurs when the temperature of the protostar gets high enough?

  Nuclear fusion begins
• What is the process called when hydrogen nuclei join to form helium?

  Nuclear fusion
• What energy is released during nuclear fusion?

  A huge amount of energy
• What two opposing forces act within a star?

  Gravity and fusion energy
• What does the force of gravity do within a star?

  Acts inwards to collapse the star
• What does the energy from nuclear fusion do within a star?

  Acts outwards to expand the star
• What is it called when the forces within a star are balanced?

  The star is in equilibrium
• What are the main components of the solar system?

  • The sun (a star)
  • Eight main planets: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune
  • Dwarf planets (e.g., Pluto)
  • Moons (natural satellites)
  • Asteroids
  • Comets